(1) Field of the Invention
The present invention relates to emulsion polymerization emulsifiers and methods of treating a mixture of tall oil fatty acids and resin acids such as found in crude or distilled tall oil with acid catalyzed formaldehyde or paraformaldehyde for use in emulsion polymerization. The improved emulsifier may be used to prepare polymers such as synthetic rubber by emulsion polymerization of monomers such as butadiene, styrene, etc.
(2) Description of the Prior Art
Tall oil is a natural mixture of resin acids and fatty acids, together with unsaponifiable materials, which is obtained by acidifying the black liquor skimmings of the sulfate process of wood pulp manufacture, using resinous woods such as pine. The composition of tall oil varies somewhat depending upon such factors as the species of the wood which was pulped. Crude tall oil acids will generally contain 18% to 60% fatty acids, 28% to 66% resin acids and 3% to 24% unsaponifiable materials. For the purpose of this invention, crude tall oil acids may be used; however, it is preferable to use distilled tall oil. The distillation may be carried out by introducing crude tall oil into a fractionation unit to separate the volatile fraction of crude tall oil from the non-volatile or pitch. Except for some separation of palmitic and more volatile acids in the first fraction, tall oil distillates have nearly the same composition as the crude tall oil. A typical tall oil distillate may contain from 25% to 66% resin acids, from 37% to 63% fatty acids and from 3% to 12% unsaponifiable materials. Various ratios of fatty acid to resin acid may be used including either the fatty acid fraction or resin acid fraction in addition to the mixed acids.
Various kinds of resin acids, such as abietic acid, palustric acid, levopimaric acid and neoabietic acid, include conjugated double bonds; and, hence these resin acids have high chemical activities. Consequently, it has been known that using alkali salt of the rosin which contains the resin acids, as emulsifier for production of synthetic rubber inhibits normal polymerization. Thus, when using rosin as an emulsifier for emulsion polymerization, it is necessary to convert the resin acid having conjugated diene structure to its derivative having no conjugated diene structure.
Polyunsaturated fatty acids, such as linoleic acid, linolenic acid and eleostearic acid, have more than one double bond in each molecular structure, as does rosin. It has been known that using polyunsaturated fatty acid containing an active methylene between nonconjugated double bonds as an emulsifier for emulsion polymerization may retard the polymerization reaction and inhibit normal progress of ordinary polymerization. When using fatty acid as an emulsion polymerization emulsifier, such fatty acid containing polyunsaturated fatty acid and mono-unsaturated fatty acid often is subjected to hydrogenation reaction so that the reaction is conducted on the polyunsaturated fatty acid to the utmost extent and not on the mono-unsaturated fatty acid. Suitable mild reaction conditions should be selected to acquire acceptable emulsifiers.
Several proposals have been made to reduce the large content of materials containing undesirable double bonds in free radical polymerization by disproportionation of the tall oil acids. In general, disproportionation is carried out by contacting tall oil with a catalyst and heating.
There are many processes in the prior art related to disproportionation reaction of tall oil in the presence of a catalyst. For examples: U.S. Pat. No. 2,617,792 discloses a method using nickel as a catalyst; U.S. Pat. Nos. 2,407,248, 2,409,173, 2,494,550, 2,497,882, and 2,503,238 disclose methods using sulfur as a catalyst; U.S. Pat. Nos. 2,311,386 and 2,503,268 disclose methods using iodine as a catalyst; U.S. Pat. No. 2,794,017 discloses a method using sulfur dioxide as a catalyst; and, more recently, U.S. Pat. No. 3,980,630 discloses a method of preparing an emulsion polymerization emulsifier comprising the steps of a disproportionation reaction of rosin, polyunsaturated fatty acid or a mixture thereof using iron iodide as a catalyst and then neutralizing the obtained product with alkali such as KOH or NaOH.
While such proposals have resulted in the repositioning of double bonds, soaps prepared from disproportioned tall oil have generally not given equivalent polymerization performance to the commonly employed partially hydrogenated-tallow fatty acid and disproportionated wood rosin soaps used in emulsion polymerization and have sometimes resulted in rubbers with appreciably lower physicals.
The lower rubber physicals in polymers produced by emulsion polymerization emulsifiers from disproportionated tall oil is often accompanied by reduced latex particle size in comparison to say a partially hydrogenated tallow--resin acid mix emulsifier. Latex production and processing are improved by producing larger, more colloidally stable rubber particles. One mechanism for accomplishing this desirable increase in latex particle size is the removal of trace impurities in the tall oil fatty acids or the mixture of tall oil fatty acids and tall oil resin acids (as in crude or distilled tall oil) which remain and which prematurely terminate the growth of individual polymer chains after disproportionation. Presumably, most of these impurities are phenolic residues from lignin which have boiling points in the tall oil range.
U.S. Pat. No. 3,528,959 teaches removal of these impurities by increasing their molecular weight by oligomerization with boron trifluoride catalyst. The crude or distilled tall oil is first disproportionated to the extent the abietic type acid content and the linoleic acid type content are reduced to less than 2% of the tall oil. This product is heated to from 149.degree. C. to 177.degree. C. in the presence of from 0.01% to 2.0% BF.sub.3 for 30 minutes to one hour; then the temperature is rapidly raised to from 249.degree. C. to 271.degree. C. to prevent degradation of the product. It is recommended for best results to distill the BF.sub.3 treated product (redistilling if the starting material was a tall oil distillate).
It has now been discovered that the disadvantageous impurities also can be deactivated in a mixture of disproportionated tall oil fatty acids and resin acids by cross-linking with formaldehyde or paraformaldehyde.
The treatment of rosin with formaldehyde is not new. U.S. Pat. No. 3,132,127 relates to improving the effectiveness of the reaction product of a rosin with formaldehyde as a raw material for the manufacture of rosin size by maintaining at a temperature of between 250.degree. C. and 300.degree. C. the reaction product of rosin with formaldehyde in the absence of an acid catalyst (at 135.degree. C. to 250.degree. C.) until the latent foaming tendency thereof has substantially decreased. U.S. Pat. No. 3,463,768 discloses that the darkening of product from using an acid catalyst and the decrease in acid number from subjecting rosin to elevated temperatures (above 250.degree. C.) are decreased when the reaction of rosin with formaldehyde is performed in two steps. In the first step, the rosin is reacted with formaldehyde between 130.degree. C. and 200.degree. C. in the absence of any strong acid. In the second step, an acid dehydration catalyst is added; and the reaction temperature is maintained between 150.degree. C. and 220.degree. C. until dehydration of the methylol groups has substantially ceased.
U.S. Pat. No. 3,681,268 discloses mastic adhesive compositions which comprise relative proportions by weight of: 100 parts of a rubber selected from the group consisting of reclaim, natural, styrenebutadiene rubbers; 50 to 200 parts by weight of a zinc salt of the formaldehyde modified rosin from reacting 2 to 10 parts by weight of formaldehyde with 100 parts by weight of molten rosin; and a hydrocarbon vehicle for the rubber.
Also, U.S. Pat. No. 3,207,743 teaches treatment of fatty acids or their esters with formaldehyde in the presence of an acid catalyst prior to epoxidation to provide plasticizers for polyvinyl chloride with improved color.
However, none of the prior art teaches acid-catalyzed formaldehyde treatment of emulsion polymerization emulsifiers from a mixture of tall oil fatty acids and resin acids.